A technique called “beamforming” has in recent years been widely known, which is used by a base station having a plurality of antenna elements to form a beam aimed at a terminal apparatus using the plurality of antenna elements. For example, Long Term Evolution (LTE) release 10 specifies that a base station is equipped with eight antennas.
According to beamforming, a beam aimed in a desired direction is formed by multiplying a signal of each antenna element by a weight coefficient. For example, in LTE, a terminal apparatus selects a recommended set from sets of weight coefficients (i.e., precoding matrices) contained in a code book, on the basis of reception of a reference signal transmitted by a base station, and notifies the base station of the recommended set. Alternatively, a base station calculates a set of weight coefficients on the basis of reception of a reference signal transmitted by a terminal apparatus.
For example, Patent Literature 1 discloses a technique of causing a terminal apparatus to transmit an uplink signal using a directional beam in order to avoid interference of the uplink signal with other signals.